1. Field of the Invention
The present invention relates to improvements in a structure for mounting and supporting a motorcycle engine on a frame. In particular, the invention relates to a motorcycle engine mounting structure by which a mounting space for the engine and freedom of design for mounting the engine is increased so that a mounting space for a radiator in a water-cooled engine may be satisfactorily ensured.
2. Description of the Prior Art
Various types of structure for mounting and supporting motorcycle engines have already been adopted.
A typical frame is provided with a front-down tube extended downwardly from a head tube and cooperating with a bracket member suspended on a middle part of the vehicle body to support a crankcase of an engine.
A cradle frame, instead of the above, is formed by connecting the above mentioned diamond frame in the lower part with a car body member and an engine is mounted and supported on the car body member connected to the downward tube.
Further, a type called a backbone frame is provided with a backbone formed of a single member extended rearwardly from a head tube. This type is used mostly for a small motorized cycle, such as a moped.
In fact, various kinds of structure for mounting and supporting an engine on a frame have been put into practice to date, but they substantially comprise improvements based on any of the above mentioned structures.
However, there have been tendencies to increase the volume of the motorcycle engine and to provide a water-cooled engine for motorcycles with such increased volume. Under these circumstances, the typical conventional frame structure mentioned above for mounting and supporting the engine has problems such as described hereinafter.
When the engine is made larger, according to the conventional frame such as the diamond type or cradle type frame wherein the front down tube is suspended or is extended rearwardly to form an enclosed space, the frame component members impose restrictions on the mounting of the engine and the width is also restricted with respect to the sitting position of the rider. It is a very difficult matter of design to mount the engine in the limited space in the front part of the frame in view of the down tube and the loop-shaped rearwardly extended member integral with the down tube. Also, when installing the engine, placement of a large engine in the down tube frame or the loop-shaped frame and connecting it with the frame therearound is difficult and complicated.
In order to solve such problems, it has been necessary to design the engine in conformity with the frame structure or taking into account the mounting workability. Thereby, the arrangements of the crankcase, transmission case and cylinder have been influenced and the engine design and power transmitting mechanism is likely to be complicated. In particular, in case a cradle type frame structure and a multi-cylinder engine are adopted, rearward extension of the exhaust pipe will be restricted by the frame and therefore a design having adverse effects on the engine performance, such as the unreasonable curving of the exhaust pipe, will have to be made.
On the other hand, with the increase of the swept volume, a water-cooled engine tends to be adopted. In such case, the cooling means for cooling water, i.e., the radiator, is arranged in the rear of the front wheel but in front of the engine. However, with the conventional type frame structure, because the down tubes are present in front of the engine, the radiator fitting space is restricted and is likely to interfere with the front wheel located in front of the radiator or with the bridge which is a turning member for steering, and also a front fork supporting member. For these reasons, it has been rather difficult to arrange the radiator and, for the arrangement of the radiator, the capacity of the radiator has had to be made as small as possible.
Further, if the radiator is set in an upper position in front of the down tubes, the steering angle will be restricted. In order to avoid this problem, the radiator must be set in the middle height or in a position somewhat lower than it. As a result, the front wheel and fender will be positioned in front of the radiator and the cooling efficiency of the cooling water will be reduced. In that case, if a cooling fan is provided in order to improve it, the space occupied by the radiator will become so large as to present a problem with respect again to the fitting space of the engine. Further, if a radiator cover is expanded sideward on the right and left so as to guide and concentrate air in the radiator, the design of the front part of the engine will become a problem. Particularly, in the motorcycle wherein the engine and radiator are exposed nakedly, the designs thereof are important and such attempt is thus undesirable.
The present invention effectively solves these problems associated with conventional structures for mounting and supporting the engine when the engine is made larger, and the structures for arranging the radiator when a water-cooled engine is adopted.